Commonly assigned, U.S. Pat. Nos. 5,388,594, 5,505,214, and 5,591,368 disclose various electrically powered smoking systems comprising electric lighters and cigarettes. The systems provide smoking pleasure while significantly reducing sidestream smoke and permitting the smoker to selectively suspend and reinitiate smoking.
The preferred embodiment of the lighter in U.S. Pat. No. 5,388,594 includes a plurality of metallic serpentine heaters disposed in a configuration that slidingly receives a tobacco rod portion of the system's cigarette. The cigarette and the lighter are configured such that when the cigarette is inserted into the lighter and as individual heaters are activated for each puff, localized charring occurs at spots about the cigarette in the locality where each heater bears against the cigarette (hereinafter referred to as a "heater footprint").
In U. S. Pat. No. 5,388,594, the sequence and the amount of energy applied to each heater element during a puff cycle is regulated by a logic circuit of a controller which executes a power subroutine upon its receiving a signal from a puff sensor. The power subroutine includes the steps of reading the voltage of the power source (batteries) at the initiation of the puff and resolving a shut-off signal in cooperation with a constant Joules energy timer such that the duration of the pulse (its cycle-period) is adjusted relative to the voltage of the power source to provide the same total amount of energy (Joules) throughout the range of voltages of the battery discharge cycle.
In U.S. Pat. No. 5,388,594, air is admitted into the interior of the heater fixture of its lighter through one or more intake ports formed at or about the seal between the cigarette and the cigarette-receiving opening of the lighter. In the alternative or in conjunction, additional ports are provided along one or more sides of the lighter housing. The air is drawn to along the cigarette.
It has been discovered in the air management system disclosed in U.S. Pat. No. 5,388,594, the ports tended to be very small if they were sized so as to create a resistance to draw commonly experienced in smoking a more traditional cigarette for a standard airflow rate of, for example, 1050 cubic centimeters per minute (cc/min). Their tiny size would necessitate precise machining in the manufacture of the lighter housing, adding expense and reducing the range of acceptable margins for error. Machining the correct diameter is exacting, because any error in diameter has a second order relation with cross-sectional area, and the latter is a determinative factor upon resistance to draw through an orifice. Accordingly, a small variation in the diameter of the intake ports can create unacceptable variations in resistance to draw in electrical lighter systems
The minute size of the ports also tended to localize or "jet" the air into the interior of the heater fixture, sometimes creating a whistling noise to the distraction of the smoker. The localization of airflow would allow some parts of the heater fixture to receive more air than others, which situation could compromise uniformity amongst consecutive executions of puff cycles.
Additionally, the dynamic range and character of drawing air through tiny ports differed from that experienced with a more traditional filter cigarette. Typically, an air intake system of an electrical lighter could be configured to approximate the resistance to draw of a more traditional filtered (lit) cigarette at a preselected (design point) draw rate; but the two systems would respond differently as a smoker would progress through a puff, which typically involves a ramping up and then down in draw rate. In comparison to the more traditional cigarettes, the prior electric lighter designs tended to create more and more excess pressure drop (resistance to draw) as a puff would progress through the higher levels of draw rate.
In U.S. Pat. No. 4,947,874 to Brooks et al, a smoking article includes a singular electrical resistance heating element that is impregnated with aerosol forming material and heated in a succession of power cycles. The article includes a current regulating circuit which provides an uninterrupted current flow immediately upon draw for about 1.5 to about 2 seconds followed by an "off" period of about 0.5 to about 1 second. The patent also proposes an alternative to an on-off time-based circuit, which alterative would include on-off and current modulating means connected to temperature sensors or other sensors that would sense either the temperature of the heating element directly or the temperature of air passing the heating element or the temperature of a second resistor having a character related to that of the aerosol carrying heating element.
The article disclosed in U.S. Pat. No. 4,947,874 is disadvantaged by its repetitively heating a singular heater and the material impregnated thereon, which creates a situation of already depleted tobacco material being heated again and again.